Thin film transistors (TFTs) are field effect transistors formed from multiple layers of thin films, such as active semiconductor layers, dielectric layers and metal electrode layers. Due to their advantages of being suitable for integration and mass production, TFTs functioning as display control units play an very important role in the field of flat panel display such as liquid crystal display (LCD), organic light emitting diode display (OLED), electronic paper display (EPD). Therefore, there is a requirement to continuously improve display performance of the TFT-integrated display panel.